1. Field of the Invention
The present invention relates to a brushless motor.
2. Description of the Related Art
In the conventional practice, motors are used as driving sources of various types of apparatuses and products. For example, the motors are used for business machines, such as printers and copying machines, various kinds of home electric appliances, and power assist sources of vehicles, such as automobiles and power-assisted bicycles. In particular, brushless motors are sometimes used as the driving sources of movable parts with high operation frequency in the light of increased durability and reduced noise.
Known as a type of such a brushless motor is an interior permanent magnet (IPM) motor where a permanent magnet is embedded in a rotor. For example, electric appliances are known in which a plurality of plate-like magnets are radially embedded in a rotor yoke and the magnets are disposed such that the same poles of adjacent magnets face each other in a circumferential direction of the yoke (see, for example, FIG. 2 of patent document 1).    [patent document 1] Japanese Translation of PCT International Application Publication No. JP2012-517209
One of the methods to improve a rotational torque of an interior permanent magnet brushless motor without increasing the motor size is to reduce the distance between the rotor and the stator. However, such an approach tends to result in increase in torque ripple and noise.